场景：Android的Webview中，javascript怎么调用java方法

Android的Webview中，javascript如何调用java方法

PS：另外推荐下面这篇文章《用注解和pojo支撑起来的轻量级REST框架--T2》

http://blog.csdn.net/nanjingjiangbiao/article/details/7680702

今天调查一个线上Bug，发现是WebView中的一小段javascript，会直接调用到后台APK的一个Java事件，最后导致java中nullpointexception。

感兴趣的是，WebView中的javascript如何调用APK中的java方法。

一个例子：

通过JS取得Android的GPS数据

第一步，WebKit的准备

首先，给与WebKit的javascript的执行许可

public void onCreate(Bundle icicle) {

super.onCreate(icicle);

WebView wv = new WebView(this);

wv.getSettings().setJavaScriptEnabled(true);//JS利用OK

setContentView(wv);

}

然后，塞入自己的javascript拦截器JsObj jo = new JsObj(this);

wv.addJavascriptInterface(jo, "roid");

第二步，定义自己的javascript拦截器

class JsObj {

private Context con;

public JsObj(Context con) {

this.con = con;

}

public String gps(String top, String end) {

LocationManager locman = (LocationManager)

con.getSystemService(Context.LOCATION_SERVICE);

Location loc = locman.getCurrentLocation("gps");

int lat = (int) (loc.getLatitude() * 1000000);

int lon = (int) (loc.getLongitude() * 1000000);

return top + "緯度:" + lat + ", 経度: " + lon + end;

}

}

第三步，定义一个可运行的html

JS on Android

document.write(roid.gps("", ""));

在这个代码里面，可以用roid.gps的方法调用第二步定义的java函数

最后，全部的代码package com.adamrocker.android.web;

import android.app.Activity;

import android.content.Context;

import android.location.Location;

import android.location.LocationManager;

import android.os.Bundle;

import android.webkit.WebView;

public class WebkitTest extends Activity {

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle icicle) {

super.onCreate(icicle);

WebView wv = new WebView(this);

wv.getSettings().setJavaScriptEnabled(true);

JsObj jo = new JsObj(this);

wv.addJavascriptInterface(jo, "roid");

setContentView(wv);

wv.loadUrl("http://www.adamrocker.com/android/js2android.html");

}

class JsObj {

private Context con;

public JsObj(Context con) {

this.con = con;

}

public String gps(String top, String end) {

LocationManager locman = (LocationManager) con

.getSystemService(Context.LOCATION_SERVICE);

Location loc = locman.getCurrentLocation("gps");

int lat = (int) (loc.getLatitude() * 1000000);

int lon = (int) (loc.getLongitude() * 1000000);

return top + "緯度:" + lat + ", 経度: " + lon + end;

}

}

}

未完

我还想知道为什么，在webview里面定义一个JSObject，就可以连接javascript和后台函数

他们之间是如何通信的？

我稍微调查了一下WebView的底层代码，webview初期化的时候/* Initialize private data within the WebCore thread.

*/

private void [More ...] initialize() {

/* Initialize our private BrowserFrame class to handle all

* frame-related functions. We need to create a new view which

* in turn creates a C level FrameView and attaches it to the frame.

*/

mBrowserFrame = new BrowserFrame(mContext, this, mCallbackProxy,

mSettings, mJavascriptInterfaces);

mJavascriptInterfaces = null;

// Sync the native settings and also create the WebCore thread handler.

mSettings.syncSettingsAndCreateHandler(mBrowserFrame);

// Create the handler and transfer messages for the IconDatabase

WebIconDatabase.getInstance().createHandler();

// Create the handler for WebStorage

WebStorage.getInstance().createHandler();

// Create the handler for GeolocationPermissions.

GeolocationPermissions.getInstance().createHandler();

// The transferMessages call will transfer all pending messages to the

// WebCore thread handler.

mEventHub.transferMessages();

// Send a message back to WebView to tell it that we have set up the

// WebCore thread.

if (mWebView != null) {

Message.obtain(mWebView.mPrivateHandler,

WebView.WEBCORE_INITIALIZED_MSG_ID,

mNativeClass, 0).sendToTarget();

}

}

生成了显示用对象mBrowserFrame

而此对象的所有操作事件，都会被mEventHub截获

而mEventHub会将请求发送给真正需要处理的MessageStub。 通过messageNameTransfer all messages to the newly created webcore thread handler.

private void [More ...] transferMessages() {

mTid = Process.myTid();

mSavedPriority = Process.getThreadPriority(mTid);

mHandler = new Handler() {

@Override

public void [More ...] handleMessage(Message msg) {

if (DebugFlags.WEB_VIEW_CORE) {

Log.v(LOGTAG, (msg.what < REQUEST_LABEL

|| msg.what

> VALID_NODE_BOUNDS ? Integer.toString(msg.what)

: HandlerDebugString[msg.what

- REQUEST_LABEL])

+ " arg1=" + msg.arg1 + " arg2=" + msg.arg2

+ " obj=" + msg.obj);

}

switch (msg.what) {

case WEBKIT_DRAW:

webkitDraw();

所以你要问我他们是怎么通信的

我只能说是线程间通信。

#以上#

1楼xiaofufu113小时前谢谢分享。